Question

The presence of only PSI, not PSII, in the bundle-sheath cells of C₄ plants has an effect on O₂ concentration. What is that effect, and how might that benefit the plant?

Short answer

No oxygen (O₂) is produced without PSII in the bundle sheath cells of C4 plants. The absence of O₂ eliminates the issue of O₂ competing with carbon dioxide (CO₂) for Rubisco binding in the bundle sheath cells.

Step-by-step solution

Meaning of PSI and PSII

The photosystem is a huge complex that comprises pigments and proteins to harvest light. They are the units of chlorophyll molecules that absorb the light energy of the sun to drive photosynthesis.

Photosystem I (PSI) and photosystem II (PSII) are the two types of photosystems (PSII). PSI is called P700, while PSII is called P680. In photosynthesis, PSII supplies PSI with high-energy electrons, which are transferred to NADP+ to form NADPH.

Effect of PSII on O2 concentration

Light is absorbed by one of PSII's pigments in the presence of sunlight. It then emits a high-energy electron, transfers it to an acceptor molecule, and replaces it with a water electron. O₂ is released as a result of the water splitting.

The function of PSII is to divide split oxygen molecules and protons as effectively as possible. As a result, the bundle sheath cells do not generate oxygen in the absence of PSII.

The absence of PSII is beneficial for C4 plants

Rubisco is an enzyme that catalyzes the reaction of RuBP (ribulose 1.5-bisphosphate) with CO₂ to produce phosphoglyceric acid, the first stage in the Calvin cycle. This enzyme, on the other hand, has a high affinity for oxygen. When there is a lot of oxygen around, it attaches to oxygen instead of carbon dioxide.

O₂ is not generated in bundle sheath cells because PSII is missing. Rubisco successfully interacts with carbon dioxide in the absence of oxygen, initiating the Calvin cycle. As a result, C4 plants benefit from the absence of PSII in bundle sheath cells.